Systems, apparatus and methods for dynamic range enhancement of audio signals

ABSTRACT

An apparatus for providing an output signal to an audio transducer comprises: one or more signal paths for receiving respective digital audio input signals, applying respective digital gains, and outputting respective amplified digital audio input signals; one or more inputs for receiving one or more volume parameters associated with the digital audio input signals; converter circuitry, coupled to the one or more signal paths, for converting the one or more amplified digital audio input signals into the analogue domain, and outputting an analogue audio input signal; an analogue gain element, for applying an analogue gain to the analogue audio input signal and outputting the output signal; and a control circuit, coupled to the one or more signal paths, operative to select the analogue gain based on a comparison of the volume parameters and the one or more digital audio input signals as multiplied by the volume parameters, and to select the respective digital gains for each digital audio input signal so that an overall gain in the respective signal path corresponds to a volume parameter associated with the respective digital audio input signal.

TECHNICAL FIELD

Examples of the present disclosure relate to the provision of audiosignals to an audio transducer, and particularly to systems, apparatusand methods using dynamic range enhancement for the provision of audiosignals to an audio transducer.

BACKGROUND

Personal audio devices, including wireless telephones, such asmobile/cellular telephones, cordless telephones, mp3 players, and otherconsumer audio devices, are in widespread use. Such personal audiodevices may include circuitry for driving a pair of headphones or one ormore speakers. Such circuitry often includes a power amplifier fordriving an audio output signal to headphones or speakers.

One particular characteristic of a personal audio device which mayaffect its marketability and desirability is the dynamic range of itsaudio output signal. Stated simply, the dynamic range is the ratiobetween the largest and smallest values of the audio output signal. Oneway to increase dynamic range is to apply a high gain to the poweramplifier. However, noise present in an audio output signal may be agenerally monotonically increasing function of the gain of theamplifier, such that any increased dynamic range as a result of ahigh-gain amplifier may be offset by signal noise which may effectivelymask lower-intensity audio signals.

Dynamic range enhancement (DRE) is a technique to mitigate these issues.DRE is a three-stage process. In a first stage, digital gain is appliedto an input digital signal; in a second stage, the digital signal isconverted to the analogue domain by converter circuitry; and, in thethird stage, an analogue gain is applied to the analogue signal. Thedigital gain may be determined dynamically, based on the amplitude ofthe input digital signal, and configured so as to increase the size ofthe digital signal at the input to the converter circuitry. In this way,the converter circuitry operates on a larger signal and as a resultconverts the signal to the analogue domain with lower noise. Theanalogue gain is configured to compensate for the digital gain, so thatoverall the signal passing through the signal path is amplified to therequired level, in spite of the dynamically changing digital gain. Thus,DRE can be used to increase the dynamic range of an audio signal.

SUMMARY

As noted above, the digital and analogue gains in a dynamic rangeenhancement process are determined based on the amplitude of the inputsignal. Where the input signal is subject to a separate path gain (e.g.,based on a volume parameter), the digital and analogue gains aredetermined based on a combination of the input signal and the signalpath, i.e. path, gain. That is, the amplitude of the input signal asaltered by the path gain is estimated and the digital and analogue gainvalues selected based on this amplitude.

The digital and analogue gains are typically quantized values, selectedfrom a plurality of possible quantized values. The ideal value of thedigital and analogue gains, calculated based on the estimated amplitude,will typically fall between their possible quantized values. Thus,selection of the digital and analogue gains will involve rounding up orrounding down from the ideal values to one of the quantized values.

In practice, to avoid the possibility of clipping (where the amplifieris overdriven by an input signal which exceeds its maximum capability),the ideal gain is always rounded up to the next quantized value.However, this can have unintended negative consequences.

In particular, where the input signal has an amplitude which is close tofull scale, the combination of the input signal and the path gain canresult in an overestimation of the analogue gain value. For example, saythe amplitude of the input signal is full scale and the path gain isalso set to a maximum value. An overestimation (or a rounding error) inthe combination of the input signal and the path gain may result in ananalogue gain value being selected which raises the noise floor in theamplified signal output by the analogue gain element of the system, andthus reduces performance.

According to one aspect of the disclosure, there is provided anapparatus for providing an output signal to an audio transducer,comprising: one or more signal paths for receiving respective digitalaudio input signals, applying respective digital gains, and outputtingrespective amplified digital audio input signals; one or more inputs forreceiving one or more volume parameters associated with the digitalaudio input signals; converter circuitry, coupled to the one or moresignal paths, for converting the one or more amplified digital audioinput signals into the analogue domain, and outputting an analogue audioinput signal; an analogue gain element, for applying an analogue gain tothe analogue audio input signal and outputting the output signal; and acontrol circuit, coupled to the one or more signal paths, operative toselect the analogue gain based on a comparison of the volume parametersand the one or more digital audio input signals as multiplied by thevolume parameters, and to select the respective digital gains for eachdigital audio input signal so that an overall gain in the respectivesignal path corresponds to a volume parameter associated with therespective digital audio input signal.

In a further aspect, the disclosure provides an electronic devicecomprising an apparatus as recited above.

Another aspect provides a method for providing an output signal to anaudio transducer, comprising: receiving one or more digital audio inputsignals, applying respective digital gains, and outputting respectiveamplified digital audio input signals; receiving one or more volumeparameters associated with the digital audio input signals; convertingthe one or more amplified digital audio input signals into the analoguedomain, and outputting an analogue audio input signal; and applying ananalogue gain to the analogue audio input signal and outputting theoutput signal. The analogue gain is determined based on a comparison ofthe volume parameters and the one or more digital audio input signals asmultiplied by the volume parameters. The respective digital gains foreach digital audio input signal are determined so that an overall gainin the respective signal path corresponds to a volume parameterassociated with the respective digital audio input signal.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of examples of the present disclosure, and toshow more clearly how the examples may be carried into effect, referencewill now be made, by way of example only, to the following drawings inwhich:

FIG. 1 shows an electronic device according to embodiments of thedisclosure;

FIG. 2 shows codec circuitry according to embodiments of the disclosure;

FIG. 3 shows codec circuitry according to further embodiments of thedisclosure;

FIG. 4 shows DRE circuitry according to embodiments of the disclosure;and

FIG. 5 is a flowchart of a method according to embodiments of thedisclosure.

DETAILED DESCRIPTION

FIG. 1 shows an electronic device 100 according to embodiments of thedisclosure. The device 100 is operable to provide high-fidelity playbackof audio, such as music, to a user of the device. In addition, thedevice may generate so-called “system sounds”, e.g., audio signalsgenerated by an operating system or other software running on thedevice, responsive to detection of an event (e.g. an incoming message orcall, an alarm, etc), or user input (e.g. button or key clicks,interaction with a game, etc). The electronic device may thereforecomprise one or more of: a portable device; a battery-powered device; acommunications device; a computing device; a mobile telephone; a laptop,notebook or tablet computer; a personal media player; a gaming device;and a wearable device.

The device 100 comprises processor circuitry 110, internal interfacecircuitry 120, an audio codec 130 and external interface circuitry 140.In general terms, according to the illustrated embodiment, multipledigital audio signals (as well as at least one volume parameter) areoutput from the processor circuitry 110, to the codec 130, via theinternal interface circuitry 120. In the codec 130, the digital audiosignals are processed, converted to the analogue domain, and amplifiedby a power amplifier. The detailed operation of the codec 130 isdescribed below. The amplified signals are then output from the codec130 and passed to the external interface circuitry 140 to be output fromthe device 100 to the user.

In the illustrated embodiment, the processing circuitry 110 and thecodec 130 are each provided on separate integrated circuits (thusrequiring internal interface circuitry 120 to effect the transfer ofdata from one to the other). In other embodiments, the functions of thecodec 130 (described below) may be provided within the AP 110 itself,i.e. on the same integrated circuit.

The processor circuitry 110 may comprise any suitable processor orprocessor circuitry for running the electronic device 100 and theapplications provided by it. For example, in one embodiment, theprocessor circuitry 110 may run an operating system and/or otherapplications provided by the electronic device. Such processor circuitrymay be known as an applications processor (AP), and the processingcircuitry 110 may also be termed the AP 110 herein.

The AP 110 is operative to output one or more digital audio signals. TheAP 110 may also output one or more volume signals associated with one ormore of the digital audio signals.

At least one of the digital audio signals (e.g. a digital signalcorresponding to music) may require high-fidelity output. Thus, in theillustrated embodiment, an audio file 112 (which may correspond to amusic file) provides a first digital audio signal. A first volumeparameter 114 is also provided by the AP 110, and is associated with theaudio file 112 in that the first volume parameter is to be applied tothe audio file before output to a user. For example, the first volumeparameter may be written in a register within or accessible by the AP110. The first volume parameter may be set based on some user input. Forexample, the user may specify the volume of music to be played from aparticular application (e.g. through interaction with the application orconfiguration settings associated with the application), or from thedevice 100 in general (e.g. through interaction with the operatingsystem or physical volume controls in the electronic device 100 or aperipheral device coupled to it).

Some embodiments of the disclosure provide for combined amplification ofa plurality of audio signals. Thus, in these embodiments, the AP 110outputs a plurality of digital audio signals. At least one other signalof the plurality of digital audio signals may relate to system sounds116, generated within the operating system or other software responsiveto detection of an event (e.g. an incoming message or call, an alarm,etc), or user input (e.g. button or key clicks, interaction with a game,etc). System sounds are generally shorter than music and therefore,relative to playback of the audio file 112, the system sounds 116 can beconsidered intermittent. It will be noted that the fidelity of systemsounds can generally be lower than that associated with music playback.

The system sounds 116 may also be associated with a volume parameter(termed herein, “the second volume parameter”) 118. Again, the secondvolume parameter may be written in a register within or accessible bythe AP 110, for example. The second volume parameter may be set based onuser input or hard-coded into the operating system. In the former case,for example, the user may specify the volume of system sounds to beplayed from a particular application or from the operating system ingeneral (e.g. through interaction with the application or configurationsettings associated with the application, or through interaction withthe operating system or configuration settings associated with theoperating system). In the latter case, the volume of system sounds maybe placed beyond the user's control.

The second volume parameter 118 may also be provided to the codec 130(and indeed FIG. 3 below describes such an embodiment). However, in theembodiment illustrated in FIG. 1 (and also in FIG. 2 below), the secondvolume parameter 118 is applied to the system sound audio signal in again element 119 within the AP 110. Thus, the output of the gain element119 is a digital audio signal, corresponding to the system sounds, towhich a volume parameter has already been applied.

It will further be understood by those skilled in the art that, althoughFIG. 1 shows a single system sounds module 116 (i.e. from which allsystem sounds are output), the various system sounds generated may beoutput separately from the AP 110. A volume parameter may be associatedwith a single system sound (i.e. a one-to-one mapping between volumeparameters and system sounds), a group of system sounds (i.e. aone-to-many mapping between volume parameters and system sounds) or allsystem sounds. In some embodiments, no volume parameter may be providedfor the system sounds, which are instead generated at the requiredvolume ab initio.

Thus, in some embodiments, one or more digital audio signals may beoutput from the AP 110 to the codec 130. The audio signals may beassociated with volume parameters or not.

The internal interface circuitry 120 may be any interface, bus or othercircuitry suitable for passing signals from one component of the device100 to another and may implement any suitable data transfer protocol.For example, the interface circuitry 120 may implement the I²S interfacestandard, and transfer pulse code modulated (PCM) signals or directstream digital (DSD) signals between the AP 110 and the codec 130.However, alternative interface standards and encoding mechanisms may beused without departing from the scope of the claims appended hereto.Those skilled in the art will realise that the disclosures herein arenot limited in that respect.

As noted above, the codec 130 is operative to receive the digital audiosignals from the AP 110, convert those digital audio signals to theanalogue domain, apply an analogue gain, and output the analogue signals(with applied gain). Detailed operation of the codec 130 is describedbelow. However, in general terms the digital audio signal 112, the firstvolume parameter 114 and the output of the gain element 119 are providedto gain and mix control circuitry (hereinafter, “control circuitry”) 132within the codec 130. The control circuitry 132 is operative to applyone or more digital gains to the respective audio signals, and tocombine the audio signals once the digital gain has been applied (inembodiments relating to amplification of a plurality of audio signals).The amplified digital audio signal is then provided to adigital-to-analogue converter (DAC) 134, which converts the signal tothe analogue domain, and the analogue signal is provided to a poweramplifier 136 for application of an analogue gain.

The control circuitry 132 is also operative to set the analogue gain inthe power amplifier 136. For example, according to embodiments of thedisclosure, the control circuitry 132 is operable to select the analoguegain based on a combination of the digital audio signals output from theAP 110, optionally after application of any volume parameter associatedwith those signals (such as the first volume parameter 114). The digitalgains applied to the digital signals may be set based on any volumeparameter associated with the digital signal and received by the codec130, adapted so as to compensate for the analogue gain applied in thepower amplifier 136.

The technical effect of this is to increase the dynamic range of theamplifier 136. In embodiments relating to amplification of a pluralityof audio signals, the technical effect is to dynamically andautomatically trade-off the dynamic range of the audio file when asystem sound is generated so as to improve the noise performance of theamplifier 136 in those circumstances. Further detail regarding thisaspect is provided below with respect to FIG. 3.

Thus, the codec 130 outputs an amplified analogue audio signal. In theillustrated embodiment, the analogue audio signal is output to externalinterface circuitry 140. For example, one or more speakers, or a set ofheadphones, or in general one or more audio transducers, may be coupledto the external interface circuitry 140. The external interfacecircuitry 140 may therefore comprise an audio plug, into which an audiojack (such as a 3.5 mm jack) or any other suitable connector (such as aLightning® connector, USB connector, etc) can be inserted.

It will further be understood that the audio transducer or transducersmay be provided within the electronic device itself (although thisembodiment is not illustrated). In such an arrangement, the analoguesignal may be provided from the codec 130 directly to the one or moreaudio transducers for playback to the user.

FIG. 2 illustrates apparatus 200 according to embodiments of thedisclosure. For example, the apparatus 200 may be suitable to providethe functions of the codec 130 described above with respect to FIG. 1.The embodiment of FIG. 2 shows amplification of a single audio signal,referred to as “SignalA”. For example, SignalA may correspond to theaudio, or music file 112, system sounds 116, the output of gain element119, a voice signal, or any combination thereof.

FIG. 2 further shows the application of a volume parameter for SignalAdenoted VolumeA.

SignalA (which is a digital audio signal) is provided on a first signalpath to a first upsampling unit 202. The upsampling unit 202 upsamplesthe signal according to a clock signal provided to it (not shown). Forexample, the signal may be upsampled from a conventional samplingfrequency for audio of 48 kHz or 192 kHz, to a higher frequency of 1.4MHz or greater. The higher sampling frequency enables changes to thedigital and analogue gains (described below) to be closely matched inthe time domain, so as to avoid “pops”, “clicks” and other unwantedartefacts which may be audible to the user.

The upsampled signal is provided to a first digital gain element 204,where a digital gain is applied.

The output of the first digital gain element 204 is provided todigital-to-analogue converter (DAC) circuitry 212, which converts thedigital signal to the analogue domain. Those skilled in the art will befamiliar with many different processes and circuits which can performthis DAC function, and the DAC circuitry 212 is not described furtherherein.

The output of the DAC circuitry 212 (which is an analogue audio signal)is provided to a power amplifier 214. The power amplifier 214 applies ananalogue gain to the signal, and outputs an amplified analogue signal toan output 216. The analogue gain is typically an attenuation of thesignal. As noted above, the amplified analogue signal may be provided toan audio transducer, either within the same electronic device as theapparatus 200 or coupled to that device.

Thus, a digital gain is applied to SignalA, before the signal isconverted to the analogue domain. An analogue gain is applied to theanalogue signal, which is then output from the apparatus 200.

In order to determine the digital gain and the analogue gain, theapparatus comprises control circuitry operable to provide controlsignals to the digital gain element 204 and the power amplifier 214 tocontrol and set the gains to be applied in those elements.

The control circuitry comprises a further digital gain element 218,which is coupled to the output of the upsampler 202 to receive theupsampled version of SignalA. The digital gain element 218 applies again to the signal which is based on the volume parameter VolumeA.

Those skilled in the art will appreciate that VolumeA and other gainfactors are often defined in terms of a logarithmic ratio (such asdecibels) between an input signal and a desired output signal. Forexample, the gain factor may define logarithmically the ratio between afull-scale input signal and a desired output signal (which may have asmaller amplitude). For example, when defined in terms of decibels, again factor of minus six (−6 dB) may be approximately equal to amultiplication factor of 0.5. The application of those logarithmic gainfactors may be effected in the digital gain element 218 and other gainelements by use of a suitable converter on the gain operand, to convertthe logarithmic value to a linear gain value, prior to themultiplication of the linear gain value with the signal. This isconventional and will be well understood by those skilled in the art.Thus, in the illustrated embodiment, each of the digital gain elements204 and 218 may comprise a suitable converter for converting thelogarithmic gain factor (i.e. defined in terms of dBs) to a linearequivalent value (see for example the converters 260, 262 describedbelow).

It will be further understood that the volume parameters and gainfactors may also be defined in terms of the direct multiplication factorto be applied to the signals in question, with suitable amendments tothe circuitry to account for the formal change.

The gain factor applied in the digital gain element 218 may further beadapted by a softramp control circuitry 220. The softramp controlcircuitry 220 may adapt the volume parameter VolumeA (which may bereceived from the AP 110, see above) so as to smooth transitions betweendifferent values of the volume parameter and avoid unwanted audioartefacts caused by any abrupt change in the volume.

In the illustrated embodiment, the softramp control circuitry 220comprises a softramp control module, which receives VolumeA (in dB) andadapts it so as to smooth transitions between different values as notedabove. The softramp control circuitry 220 further comprises a dB tolinear converter module, which converts the output of the softrampcontrol module from dB to a linear multiplication value to be applied inthe digital gain element 218.

The output of the gain element 218, which is equal to SignalA*VolumeA(subject to smoothing by the softramp control module), is provided toDRE circuitry 228.

According to embodiments of the disclosure, the DRE circuitry 228 isoperative to provide an analogue gain parameter AVOL to the poweramplifier 214. In one embodiment, the analogue gain parameter is basedon the output of the digital gain element 218, i.e. SignalA*VolumeA.

In more detail, the DRE circuitry 228 comprises converter circuitry 250for converting the linear output of the digital gain element 218 to dB.In the illustrated embodiment, the converter circuitry comprises alook-up table (LUT) between the linear values and corresponding dBvalues, but those skilled in the art will be well aware of alternativeconversion mechanisms and the present disclosure is not limited in thatregard.

The output of the converter circuitry is provided to a DRE core module252, which performs one or more functions based on the output of theconverter circuitry, and outputs an analogue gain parameter. Forexample, the DRE core module 252 may apply one or more filters to theoutput of the converter circuitry 250 so as to condition the signal toachieve a desired effect. The filters may comprise a low-pass filter,designed to smooth the signal by filtering out high-frequencycomponents, for example. The DRE core module 252 may additionally oralternatively detect an envelope of the output of the convertercircuitry 250, SignalA*VolumeA, and output the envelope as the analoguegain parameter. The output of the DRE core module 252 (whethercorresponding to the filtered output of the converter circuitry 250and/or the envelope of that output) may be subject to one or moreadditional operations, such as the addition of an offset to provide afixed amount of padding or headroom to account for any underestimationin the output.

According to the principles of dynamic range enhancement, the analoguegain parameter output by the DRE core module 252 would be provided tothe power amplifier 214 for use as the analogue gain to be applied tothe output of the DAC circuitry 212. The analogue gain parameter wouldalso be combined with VolumeA (e.g., through subtraction of the analoguegain parameter from VolumeA), to determine the digital gain to beapplied in the digital gain element 204.

However, as noted above, this arrangement has the disadvantage ofraising the noise floor in certain circumstances, where SignalA or itscombination with VolumeA are overestimated. For example, quantizationerror may be introduced in any of the dB-to-linear or linear-to-dBconvertor mechanisms 250, 262, or in the detection of the envelope inthe DRE core 252. This can result in the analogue gain parameterexceeding the path gain (VolumeA), raising the noise floor and reducingperformance.

In order to address this problem, according to embodiments of thedisclosure the DRE circuitry 228 additionally comprises limitercircuitry configured to limit the analogue gain parameter to whicheveris smaller of the output of the DRE core module (e.g., SignalA*VolumeA)and the path gain (e.g., VolumeA). In this way, the analogue gain isconstrained never to exceed the path gain, maintaining an optimal noisefloor for full-scale input signals and preventing underestimation of theinput signal at all amplitudes.

In the illustrated embodiment, the limiter circuitry comprises aselector module 254 which is configured to receive as inputs the outputof the DRE core module 252 (e.g., SignalA*VolumeA) and the path gainfrom the softramp control module 264 (e.g., VolumeA). The DRE circuitry228 further comprises a minimum detection module 256, which is alsoconfigured to receive as inputs the output of the DRE core module 252(e.g., SignalA*VolumeA) and the path gain from the softramp controlmodule 264 (e.g., VolumeA), and to determine which is smaller. Theminimum detection module 256 outputs a control signal to the selectormodule 254, indicative of the smaller signal, and the selector module254 is then operative to output the smaller signal as the analogue gainparameter.

The analogue gain parameter (AVOL) is provided to the power amplifier214 for application as the analogue gain to the output of the DACcircuitry 212. The analogue gain parameter may be subject to a delay(e.g., in a delay unit 258 as shown in FIG. 2), to account for delay inthe DAC circuitry 212, such that a particular value of the analogue gainis applied to a signal on the digital components of which the analoguegain was determined.

The analogue gain parameter is also provided to a combining element 230to be used in determining the digital gain to be applied in the digitalgain element 204. The analogue gain AVOL so provided may not be subjectto the same delay applied to the analogue gain AVOL provided to thepower amplifier 214, as the digital gains are applied prior to theprocessing in DAC circuitry 212.

Further, the analogue gain parameter is linear in some embodiments. Whenprovided to the combining element 230, however, the quantity may beconverted back to a logarithmic equivalent (i.e. dBs) in dB-to-linearconvertor circuitry 260.

The combining element 230 thus receives the volume parameter VolumeA (orthe output of the softramp control module 220), the analogue gain fromDRE circuitry 228, and outputs a signal equal to the difference, e.g.,VolumeA−AVOL. So, for example, if VolumeA is −6 dB, and AVOL is −1 dB,then the digital gain factor applied in combining element 330 is −5 dB.

The output of the combining element 230 is the digital gain factor to beapplied to SignalA. Thus, the output of combining element 230 isprovided to digital gain element 204, and a digital gain factor equal toVolumeA−AVOL is applied to SignalA.

It will be noted that the analogue gain applied in the power amplifier214 (i.e. to the combination of audio signals) is thus effectivelycompensated for by corresponding alterations in the digital gainsapplied to each signal individually. The net effect of this circuitry isthat SignalA is preserved when it is the sole audio signal, maximizingthe dynamic range of the amplifier 214 using an analogue volume.Further, by limiting the analogue gain to the minimum of the path gainand the output of the digital gain element 218, an optimal noise flooris maintained for full-scale input signals without causingunderestimation of the input signal at other amplitudes.

The circuitry of FIG. 2 thus shows the application of dynamic rangeenhancement to a signal audio signal according to embodiments of thedisclosure. High-quality audio playback is clearly a desirable featurefor personal audio devices. However, such devices are becomingincreasingly multi-functional, such that audio playback is only one ofseveral functions which may be provided simultaneously by the device.For example, in a typical operating system there may be a variety ofaudio streams which can be classified into two groups: music (HiFi) andsystem sounds (keyclicks, alarms, ringtones). These different soundsmust be mixed together into a single output audio stream.

It is therefore desirable to apply dynamic range enhancement also tocombinations of multiple audio signals, each of which may be subject totheir own respective volume parameters.

FIG. 3 illustrates an apparatus 300 according to embodiments of thedisclosure in which multiple audio signals are combined. For example,the apparatus 300 may be suitable to provide the functions of the codec130 described above with respect to FIG. 1.

It will be apparent from the description below that the apparatuscomprises a first signal path for receiving a first digital audio inputsignal, applying a first digital gain, and outputting an amplified firstdigital audio input signal, and a second signal path, for receiving asecond digital audio input signal, applying a second digital gain, andoutputting an amplified second digital audio input signal. Convertercircuitry converts the amplified first and second digital audio inputsignals into the analogue domain, and outputs an analogue audio inputsignal, and an analogue gain element applies an analogue gain to theanalogue audio input signal and outputting the output signal. Theanalogue gain is determined based on a combination of at least the firstand second digital audio input signals or signals derived therefrom(such as where one or more of the first and second digital audio inputsignals is multiplied by a respective volume parameter). The first andsecond digital gains are selected so as to compensate for the analoguegain. In such a manner, dynamic range enhancement may be applied to thefirst digital audio input signal in the absence of the second digitalaudio input signal, while allowing for trade-off of the dynamic rangewhen the second digital audio input signal is present.

Further, according to embodiments of the disclosure, the analogue gainis limited to the minimum of the combination of at least the first andsecond digital audio input signals or signals derived therefrom (such aswhere one or more of the first and second digital audio input signals ismultiplied by a respective volume parameter), and the maximum path gainof at least the first and second signal paths. In other words, theanalogue gain is limited to whichever is smaller of:

-   -   the combination of at least the first and second digital audio        input signals or signals derived therefrom; and    -   a summation of all path gains (e.g., in the linear domain)

In FIG. 3, two signal paths are illustrated: “SignalA” (which may betaken to correspond substantially to the audio, or music file 112);“SignalB” (which may be taken to correspond substantially to systemsounds 116, or the output of gain element 119, as described above). Asnoted above, however, more than two signal paths may be provided inorder to combine more than two audio signals. For example, an audiosignal may be provided comprising voice data. The concepts disclosedherein are not limited in that respect. In general herein, any two ormore audio streams, of any frame rate and/or bit width, may be combinedaccording to the principles disclosed herein.

Further, FIG. 3 shows the application of respective volume parametersfor SignalA and SignalB, denoted VolumeA and VolumeB. However, in someembodiments, only one volume parameter (i.e. for one of the signals) maybe provided to the apparatus. For example, FIG. 2 illustrates anembodiment in which a volume is applied to an audio signal within the AP210, i.e. outside the codec 230 and the apparatus 300. In that case, theVolumeB parameter of FIG. 3 may be ignored.

Thus SignalA (which is a digital audio signal and may be representativeof music or some other signal requiring high-fidelity output) isprovided on a first signal path to a first upsampling unit 302. Theupsampling unit 302 upsamples the signal according to a clock signalprovided to it (not shown). For example, the signal may be upsampledfrom a conventional sampling frequency for audio of 48 kHz or 192 kHz,to a higher frequency of 1.4 MHz or greater. The higher samplingfrequency enables changes to the digital and analogue gains (describedbelow) to be closely matched in the time domain, so as to avoid “pops”,“clicks” and other unwanted artefacts which may be audible to the user.The upsampled signal is provided to a first digital gain element 304,where a first digital gain is applied.

Similarly, SignalB (which is a digital audio signal, and may berepresentative of system sounds or some other signal not requiringhigh-fidelity output) is provided on a second signal path to a secondupsampling unit 306. The upsampling unit 306 upsamples the signal in asimilar manner to the upsampling unit 302, and the upsampled signal isprovided to a second digital gain element 308, where a second digitalgain is applied.

The outputs of the first and second digital gain elements 304, 308 aresummed in a summing element 310, and provided to digital-to-analogueconverter (DAC) circuitry 312, which converts the summed digital signalto the analogue domain. Those skilled in the art will be familiar withmany different processes and circuits which can perform this DACfunction, and the DAC circuitry 312 is not described further herein.

The output of the DAC circuitry 312 (which is an analogue audio signal)is provided to a power amplifier 314. The power amplifier 314 applies ananalogue gain to the signal, and outputs an amplified analogue signal toan output 316. The analogue gain is typically an attenuation of thesignal. As noted above, the amplified analogue signal may be provided toan audio transducer, either within the same electronic device as theapparatus 300, or coupled to that device.

Thus first and second digital gains are applied to SignalA and SignalB,before the signals are combined and converted to the analogue domain. Ananalogue gain is applied to the analogue signal, which is then outputfrom the apparatus 300. Those skilled in the art will appreciate thatalternative circuitry may be provided which achieves substantially thesame effect. For example, both FIGS. 2 and 3 show the application ofdigital gain to the first and second digital audio signals, and thecombination of those digital signals prior to conversion to the analoguedomain (in the control circuitry 234 or the combining element 310).However, it will be apparent that the digital signals may be convertedto the analogue domain separately, and then combined, without alteringthe operation of the circuitry significantly and without departing fromthe scope of the claims appended hereto.

In order to determine the first and second digital gains, and theanalogue gain, which are to be applied to the various signals in theapparatus 300, the apparatus comprises control circuitry operable toprovide control signals to the first and second digital gain elements304, 308 and the power amplifier 314 to control and set the gains to beapplied in those elements.

The control circuitry comprises a further digital gain element 318,which is coupled to the output of the upsampler 302 to receive theupsampled version of SignalA. The digital gain element 318 applies again to the signal which is based on the volume parameter VolumeA.

As described above, the gain applied in the digital gain element 318 istypically a linear value, and therefore VolumeA may have first beenconverted from dB to a linear value. Again, the gain factor applied inthe digital gain element 318 may further be adapted by a softrampcontrol module 320. The softramp control module 320 may adapt the volumeparameter VolumeA (which may be received from the AP 110, see above) soas to smooth transitions between different values of the volumeparameter and avoid unwanted audio artefacts caused by any abrupt changein the volume.

Similarly, the control circuitry comprises another digital gain element322, coupled to the output of the upsampler 306 to receive the upsampledversion of SignalB. The digital gain element 322 applies a gain to thesignal which is based on the volume parameter VolumeB (which may also beprovided from the AP 110 or accessible in a register). Again, the volumeparameter VolumeB may be further adapted by a softramp control module324, similar to the module 320.

The outputs of the gain elements 318, 322 are provided to a combiningelement 326, which sums them and provides the summed output to DREcircuitry 328. Thus, the DRE circuitry 328 receives a signal which isequal to (SignalA*VolumeA+SignalB*VolumeB), wherein the operator *relates to application of a gain (i.e. defined in terms of decibels)rather than direct multiplication of two quantities, as noted above. Forexample, if SignalA and SignalB are both equal to 1, VolumeA is equal to−6 dB and VolumeB is equal to −9 dB, the DRE circuitry 328 receives asignal which is approximately equal to 0.5+0.35=0.85.

The DRE circuitry 328 determines an analogue gain parameter AVOL to thepower amplifier 314, which is based on a combination of SignalA andSignalB or signals derived therefrom. In one embodiment, the analoguegain may be set to (SignalA*VolumeA+SignalB*VolumeB), i.e. the output ofthe combining element 326. However, as noted above, this configurationmay lead to unwanted raised noise levels when the input signals are ator close to full scale.

FIG. 4 thus shows DRE circuitry 400 according to embodiments of thedisclosure, for controlling amplification and applying dynamic rangeextension to combinations of multiple input audio signals. The DREcircuitry 400 may thus perform the functions of the DRE circuitry 328shown in FIG. 3.

The DRE circuitry 400 comprises converter circuitry 450 for convertingthe linear output of the digital gain element 318 to dB. In theillustrated embodiment, the converter circuitry comprises a look-uptable (LUT) between the linear values and corresponding dB values, butthose skilled in the art will be well aware of alternative conversionmechanisms and the present disclosure is not limited in that regard.

The output of the converter circuitry is provided to a DRE core module452, which performs one or more functions based on the output of theconverter circuitry, and outputs an analogue gain parameter. Forexample, the DRE core module 452 may apply one or more filters to theoutput of the converter circuitry 450 so as to condition the signal toachieve a desired effect. The filters may comprise a low-pass filter,designed to smooth the signal by filtering out high-frequencycomponents, for example. The DRE core module 452 may additionally oralternatively detect an envelope of the output of the convertercircuitry 450, SignalA*VolumeA+SignalB*VolumeB, and output the envelopeas the analogue gain parameter. The output of the DRE core module 452(whether corresponding to the filtered output of the converter circuitry450 and/or the envelope of that output) may be subject to one or moreadditional operations, such as the addition of an offset to provide afixed amount of padding or headroom to account for any underestimationin the output.

According to embodiments of the disclosure the DRE circuitry 400additionally comprises limiter circuitry configured to limit theanalogue gain parameter to whichever is smaller of the output of the DREcore module 452 (e.g., SignalA*VolumeA+SignalB*VolumeB) and thesummation of the path gains in the first and second signal paths (e.g.,VolumeA+VolumeB). In this way, the analogue gain maintains an optimalnoise floor for full-scale input signals and preventing underestimationof the input signal at all amplitudes.

In the illustrated embodiment, the limiter circuitry comprises a firstdB to linear converter 462 which is configured to receive as input thepath gain from softramp control circuitry 320 (e.g., VolumeA), and toconvert that signal from dB to the linear domain. Of course, theconversion to the linear domain may alternatively take place outside theDRE core module 400. The DRE circuitry 400 further comprises a second dBto linear converter 464 which is configured to receive as input the pathgain from softramp control circuitry 324 (e.g., VolumeB), and to convertthat signal from dB to the linear domain. Again, the conversion to thelinear domain may alternatively take place outside the DRE core module400. The two linear numbers are then summed in a summing element 466,and converted back to decibels in converter circuitry 468 (which may bea dB LUT, similar to circuitry 450, or a different mechanism).

The limiter circuitry further comprises a selector module 454 which isconfigured to receive as inputs the output of the DRE core module 452(e.g., SignalA*VolumeA+SignalB*VolumeB) and the output of the convertercircuitry 468 (e.g., VolumeA+VolumeB). These signals are furtherprovided to a minimum detection module 456, which is configured todetermine which is smaller. The minimum detection module 456 outputs acontrol signal to the selector module 454, indicative of the smallersignal, and the selector module 454 is then operative to output thesmaller signal as the analogue gain parameter.

The analogue gain parameter (AVOL) is provided to the power amplifier314 for application as the analogue gain to the output of the DACcircuitry 312. The analogue gain parameter may be subject to a delay(e.g., in a delay unit 458 as shown in FIG. 4), to account for delay inthe DAC circuitry 312, such that a particular value of the analogue gainis applied to a signal on the digital components of which the analoguegain was determined.

The analogue gain parameter is also provided to first and secondcombining elements 330, 332 to be used in determining the first andsecond digital gains to be applied in the first and second digital gainelements 304, 308. The analogue gain AVOL so provided may not be subjectto the same delay applied to the analogue gain AVOL provided to thepower amplifier 314, as the digital gains are applied prior to theprocessing in DAC circuitry 312.

Further, the analogue gain parameter is linear in some embodiments. Whenprovided to the combining elements 330, 332, however, the quantity maybe converted back to a logarithmic equivalent (i.e. dBs) in dB-to-linearconvertor circuitry 460.

One combining element 330 receives the volume parameter VolumeA (or theoutput of the softramp control module 320), the analogue gain from DREcircuitry 328, and outputs a signal equal to the difference, e.g.,VolumeA−AVOL. The other combining element 332 receives the volumeparameter VolumeB (or the output of the softramp control module 324),the analogue gain from DRE circuitry 328, and outputs a signal equal tothe difference, e.g., VolumeB−AVOL. So, for example, if VolumeA is −6dB, and AVOL is −1 dB, then the digital gain factor applied in combiningelement 330 is −5 dB. Similarly, if VolumeB is −9 dB, and AVOL is −1 dB,then the digital gain factor applied in combining element 332 is −8 dB.

The outputs of the combining elements 330, 332 are the digital gainfactors to be applied to SignalA and SignalB. Thus, the output ofcombining element 330 is provided to digital gain element 304, and adigital gain factor equal to VolumeA−AVOL is applied to SignalA. Theoutput of combining element 332 is provided to digital gain element 308,and a digital gain factor equal to VolumeB−AVOL is applied to SignalB.

It will be noted that the analogue gain applied in the power amplifier314 (i.e. to the combination of audio signals) is thus effectivelycompensated for by corresponding alterations in the digital gainsapplied to each signal individually. The net effect of this circuitry isthat SignalA is preserved when it is the sole audio signal, maximizingthe dynamic range of the amplifier 314 using an analogue volume. WhenSignalB is added (such as a system sound), the dynamic range of SignalAis traded off via digital attenuation. The changes in digital andanalogue gain factors may be closely correlated to ensure that audibleartefacts arising from the dynamically changing gain factors are reducedor eliminated entirely. Further, by limiting the analogue gain to theminimum of the summation of the volume parameters and the output of thecombining element 326, an optimal noise floor is maintained forfull-scale input signals without causing underestimation of the inputsignals at other amplitudes.

FIG. 5 is a flowchart of a method according to embodiments of thedisclosure. The method may be carried out in a codec, such as the codec130 or either apparatus 200 or 300 described above.

The method begins in step 500, in which one or more digital audio inputsignals are obtained. The signals may be generated within the codec orprovided to the codec from another device. According to the method, theone or more digital audio input signals are subject to digital gains,and their combination (in the analogue domain) is subject to an analoguegain. Thus, the method comprises a process of determining theappropriate gains and a process of applying those gains, which processesmay be conducted in parallel.

One or more of the digital audio input signals may be associated withvolume parameters, also provided to the codec or accessible by thecodec. In step 502, in order to determine the appropriate gains, therelevant volume parameters are applied to the digital audio inputsignals as digital gain factors. If no volume parameter is defined for aparticular digital audio input signal, no gain factor is applied in thisstep.

In step 504, one or more digital gains and an analogue gain aredetermined based on the output of step 502. For example, the analoguegain may be determined based on a comparison of the volume parameters tothe signal(s) output from step 502. The analogue gain may be determinedas whichever is smaller of: a summation of the one or more volumeparameters; and a combination of the one or more digital audio inputsignals as multiplied by the respective volume parameters (thecombination may be a summation, for example).

Where a plurality of volume parameters are received as part of themethod, the analogue gain may be determined based on a comparison of thesummation of the plurality of volume parameters (e.g., in the lineardomain) and the one or more digital audio input signals as multiplied bythe volume parameters. If more than one digital audio input signal isreceived in step 500 (e.g., first and second digital audio inputsignals), the analogue gain may be determined based on a comparison ofthe summation of the volume parameters and a combination of the firstand second digital audio input signals as multiplied by the volumeparameters. The combination may comprise a summation of the first andsecond digital audio input signals as multiplied by the volumeparameters.

The digital gain for a digital audio input signal may be determined as adifference between the volume associated with the digital audio inputsignal and the analogue gain.

In step 506, the digital gains are applied to the one or more digitalaudio input signals. For example, where only a single digital audioinput signal is obtained, a single digital gain is applied to thatsignal; where more than one digital audio input signal is obtained,respective digital gains may be applied to those signals.

In step 508, the one or more digital audio input signals, afterapplication of the digital gains, are converted to the analogue domainin a single analogue signal. For example, where step 500 comprisesobtaining first and second digital audio input signals, afterapplication of the digital gain(s), the first and second digital audioinput signals may be combined into a combined digital signal beforeconversion to a corresponding analogue signal. Alternatively, the firstand second digital audio input signals may each be converted torespective analogue signals before being combined. Where step 500comprises obtaining a single digital audio input signal, that digitalsignal may be converted directly to a corresponding analogue signalafter application of the digital gain.

In step 512, the analogue gain determined in step 504 is applied to thecombined analogue signal, for example in a power amplifier. Theconversion in step 508 may introduce some delay to the signals, andtherefore the analogue gain may also be delayed by a correspondingamount in step 510, to ensure that the correct gain is applied to thecorrect signal.

The present disclosure thus provides methods, apparatus and systems forthe output of an audio signal to an audio transducer. In particular, theconcepts disclosed herein utilize dynamic range enhancement techniquesto improve or maximize the dynamic range of an audio signal, whileensuring that the noise floor is not raised for full-scale inputsignals.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. The word “comprising” does not excludethe presence of elements or steps other than those listed in a claim,“a” or “an” does not exclude a plurality, and a single feature or otherunit may fulfil the functions of several units recited in the claims.Any reference numerals or labels in the claims shall not be construed soas to limit their scope. Terms such as amplify or gain include possiblyapplying a scaling factor of less than unity to a signal.

As used herein, when two or more elements are referred to as “coupled”to one another, such term indicates that such two or more elements arein electronic communication or mechanical communication, as applicable,whether connected indirectly or directly, with or without interveningelements.

This disclosure encompasses all changes, substitutions, variations,alterations, and modifications to the example embodiments herein that aperson having ordinary skill in the art would comprehend. Similarly,where appropriate, the appended claims encompass all changes,substitutions, variations, alterations, and modifications to the exampleembodiments herein that a person having ordinary skill in the art wouldcomprehend. Moreover, reference in the appended claims to an apparatusor system or a component of an apparatus or system being adapted to,arranged to, capable of, configured to, enabled to, operable to, oroperative to perform a particular function encompasses that apparatus,system, or component, whether or not it or that particular function isactivated, turned on, or unlocked, as long as that apparatus, system, orcomponent is so adapted, arranged, capable, configured, enabled,operable, or operative. Accordingly, modifications, additions, oromissions may be made to the systems, apparatuses, and methods describedherein without departing from the scope of the disclosure. For example,the components of the systems and apparatuses may be integrated orseparated. Moreover, the operations of the systems and apparatusesdisclosed herein may be performed by more, fewer, or other componentsand the methods described may include more, fewer, or other steps.Additionally, steps may be performed in any suitable order. As used inthis document, “each” refers to each member of a set or each member of asubset of a set.

Although exemplary embodiments are illustrated in the figures anddescribed below, the principles of the present disclosure may beimplemented using any number of techniques, whether currently known ornot. The present disclosure should in no way be limited to the exemplaryimplementations and techniques illustrated in the drawings and describedabove.

Unless otherwise specifically noted, articles depicted in the drawingsare not necessarily drawn to scale.

All examples and conditional language recited herein are intended forpedagogical objects to aid the reader in understanding the disclosureand the concepts contributed by the inventor to furthering the art, andare construed as being without limitation to such specifically recitedexamples and conditions. Although embodiments of the present disclosurehave been described in detail, it should be understood that variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the disclosure.

Although specific advantages have been enumerated above, variousembodiments may include some, none, or all of the enumerated advantages.Additionally, other technical advantages may become readily apparent toone of ordinary skill in the art after review of the foregoing figuresand description.

To aid the Patent Office and any readers of any patent issued on thisapplication in interpreting the claims appended hereto, applicants wishto note that they do not intend any of the appended claims or claimelements to invoke 35 U.S.C. § 112(f) unless the words “means for” or“step for” are explicitly used in the particular claim.

The invention claimed is:
 1. An apparatus for providing an output signalto an audio transducer, comprising: one or more signal paths forreceiving respective digital audio input signals, applying respectivedigital gains, and outputting respective amplified digital audio inputsignals; one or more inputs for receiving one or more volume parametersassociated with the digital audio input signals; converter circuitry,coupled to the one or more signal paths, for converting the one or moreamplified digital audio input signals into the analogue domain, andoutputting an analogue audio input signal; an analogue gain element, forapplying an analogue gain to the analogue audio input signal andoutputting the output signal; and a control circuit, coupled to the oneor more signal paths, operative to select the analogue gain based on acomparison of the volume parameters and the one or more digital audioinput signals as multiplied by the volume parameters, and to select therespective digital gains for each digital audio input signal so that anoverall gain in the respective signal path corresponds to a volumeparameter associated with the respective digital audio input signal. 2.The apparatus according to claim 1, wherein the control circuit isoperative to select as the analogue gain whichever is smaller of: asummation of the one or more volume parameters; and a combination of theone or more digital audio input signals as multiplied by the respectivevolume parameters.
 3. The apparatus according to claim 2, wherein theone or more volume parameters are summed in a linear domain.
 4. Theapparatus according to claim 2, wherein the one or more inputs receive asingle volume parameter.
 5. The apparatus according to claim 2, whereinthe combination comprises a summation of the one or more digital audioinput signals as multiplied by the volume parameters.
 6. The apparatusaccording to claim 1, wherein the apparatus comprises first and secondsignal paths for receiving respective first and second digital audioinput signals, and wherein the control circuit is operative to selectthe analogue gain based on a comparison of the summation of the one ormore volume parameters and a combination of the first and second digitalaudio input signals as multiplied by the volume parameters.
 7. Theapparatus according to claim 6, wherein the second digital audio inputsignal is intermittent, such that the analogue gain and a first digitalgain applied to the first digital audio input signal are selected so asto compensate for the presence and absence of the second digital audioinput signal.
 8. The apparatus according to claim 1, wherein theanalogue gain is configured with a delay to compensate for delay causedby the converter circuitry.
 9. The apparatus according to claim 1,wherein at least one of the one or more digital audio input signals is afull-amplitude signal.
 10. The apparatus according to claim 1, whereinthe analogue gain is selected such that a bit width of a combination ofat least the amplified digital audio input signals matches a capacity ofthe converter circuitry.
 11. The apparatus according to claim 1, whereinthe apparatus is provided on a single integrated circuit.
 12. Anelectronic device comprising: an apparatus as claimed in claim
 1. 13.The electronic device according to claim 12, further comprisingprocessor circuitry, configured to provide to the apparatus one or moreof: the one or more digital audio input signals; and the one or morevolume parameters.
 14. The electronic device according to claim 12,wherein the electronic device is at least one of: a portable device; abattery powered device; a communications device; a computing device; amobile telephone; a laptop, notebook or tablet computer; a personalmedia player; a gaming device; and a wearable device.
 15. A method forproviding an output signal to an audio transducer, comprising: receivingone or more digital audio input signals, applying respective digitalgains, and outputting respective amplified digital audio input signals;receiving one or more volume parameters associated with the digitalaudio input signals; converting the one or more amplified digital audioinput signals into the analogue domain, and outputting an analogue audioinput signal; and applying an analogue gain to the analogue audio inputsignal and outputting the output signal, wherein the analogue gain isdetermined based on a comparison of the volume parameters and the one ormore digital audio input signals as multiplied by the volume parameters,and wherein the respective digital gains for each digital audio inputsignal are determined so that an overall gain in the respective signalpath corresponds to a volume parameter associated with the respectivedigital audio input signal.
 16. The method according to claim 15,wherein the analogue gain is determined as whichever is smaller of: asummation of the one or more volume parameters; and a combination of theone or more digital audio input signals as multiplied by the respectivevolume parameters.
 17. The method according to claim 16, wherein the oneor more volume parameters are summed in a linear domain.
 18. The methodaccording to claim 15, wherein first and second digital audio inputsignals are received, and wherein the analogue gain is determined basedon a comparison of the summation of the one or more volume parametersand a combination of the first and second digital audio input signals asmultiplied by the volume parameters.
 19. The method according to claim18, wherein the combination comprises a summation of the first andsecond digital audio input signals as multiplied by the volumeparameters.
 20. The method according to claim 18, wherein the seconddigital audio input signal is intermittent, such that the analogue gainand a first digital gain applied to the first digital audio input signalare selected so as to compensate for the presence and absence of thesecond digital audio input signal.